The intake and exhaust valves of most engines are actuated by a mechanical linkage operatively coupled to a camshaft of the engine. The camshaft is mechanically coupled to a crankshaft of the engine by either gears or belts. The crankshaft is further coupled to a piston which allows the motion of the valves to be synchronized with the motion of the piston. A disadvantage of this type of valve actuation is that timing and duration of valve events, i.e. the opening and closing of the valves, is fixed relative to the position of the piston and cannot be adjusted for varying engine operating conditions.
One method to vary the timing and duration of valve events is to actuate the valves with an actuator which operates independently of the camshaft. These actuators open and close the valves in response to an electronic control signal generated by an engine controller. These actuators can either be electrical actuators which utilize electrical power to open the valve or hydro-electrical actuators which utilizes an electrical solenoid to control the flow of pressurized fluid used to open the valve. A spring then returns the valve to the closed position when the electronic control signal is not recieved. Both actuators allow the intake valve or exhaust valve to be opened at any time during the stroke of the piston in response to the receipt of the control signal. Thus, timing and duration of valve events may be varied by altering the electronic control signal. By varying the timing and duration of the valve events, performance and emissions can be better optimized for different engine operating conditions.
However, a drawback to actuating the valves with this type of actuator is that the valves can be placed in an open position when the piston is near its uppermost position. If the intake or exhaust valve is positioned in the open position when the piston is in the uppermost position, the valve will interfere, or come into contact with, the piston. When the valve interferes with the piston, the resulting collision usually damages the valve and actuator. Valve interference is generally not a problem with camshaft actuated valves. Camshaft actuated valves are mechanically configured such that the intake and exhaust valves are positioned in the closed position when the piston is in its uppermost position thereby making it impossible for the valves to interfere with the piston.
What is needed therefore is a method and apparatus which prevents interference between the piston and the valves in an engine using electronically controlled valve actuators.